In general, olfactory receptor neurons (ORNs) are bipolar with an apical dendrite containing cilia or microvilli and a basal unmyelinated axon. In the squid, Lolliguncula brevis, five morphological variations on this general theme have been described. Preliminary data suggests a correlation between morphology and metabolite profiles in squid ORNs. Previous work in our lab has shown that a single squid ORN responds to two odors with opposing currents, suggesting activation of different odorant receptors and signal transduction pathways. Thus, this application is based on the hypotheses that: 1) squid ORN subtypes will have different but overlapping odor specificities; and 2) regardless of ORN subtype, odor-evoked excitatory responses will use a cAMP-mediated transduction pathway. Specific Aim 1 will establish the odor specificities of squid ORN subtypes. Specific Aim 2 will show that odors eliciting a depolarizing response in squid ORN subtypes are transduced by the same cAMP-mediated transduction pathway. Data will be analyzed for correlation between the transduction pathway, ORN metabolite profile, and odor specificities. The sense of smell contributes greatly to quality of life and is important as a warning against spoiled foods, gas leaks, or smoke. Recently, there have been several studies correlating the loss of smell with early onset of Alzheimer's and Parkinson's diseases. These diseases imply that there is a greater need to understand the olfactory system.